Detentions are happening for two reasons.
The first is less common - not doing homework. He is reminded nightly to get his homework done, help is offered, we can see exactly what is due and when but sometimes it slips through the net and he doesn't do it and then he gets a detention for it.
The other, more common, reason is for "reprimands" - a teacher can sign his handbook for anything like not listening, being cheeky, general pissing about, uniform breeches, etc and five "reprimands" gets a detention.
The trouble is, there's no mechanism for the teachers to specify what they are signing for so when I check his book and see five signatures, I can't tell exactly what he's done and the school can't tell me either. When I ask him, he just says they are for little things like not tucking in his shirt, or messing about with his friends when he should be doing something else.
And I know it sounds petty but I tell him every bloody morning to tuck his goddamn shirt in and he never does.
Anyway, last night after he came home having got a detention for five reprimands, I took his phone for the evening and he came down this morning with his shirt tucked in so it's had some effect.